Prior to the present invention, as shown by Ryang, for Silylnorbornane Anhydrides and Methods for Making, U.S. Pat. No. 4,381,396, assigned to the same assignee as the present invention and incorporated herein by reference, silylnorbornane anhdyrides were made by effecting reaction between 5-norbornene-2,3-carboxylic anhydride and a silicon hydride in the presence of a platinum catalyst. As taught by Ryang, anhydride terminated polydiorganosiloxane was made by equilibrating the 1,3-bis(norbornane-dicarboxylic anhydride)(tetraorganodisiloxane with cyclopolydiorganosiloxane in the presence of an organic solvent such as toluene and an equilibration catalyst such as sulfuric acid. Although valuable results can be achieved by Ryang in accordance with the aforementioned equilibration procedure, experience has shown that when equilibration is conducted in the presence of an organic solvent, a significant amount of cyclopolydiorganosiloxane is generated, which can be up to 99% by weight of the initial diorganosiloxane utilized mixture. It would be desirable to make norbornane anhydride substituted organosiloxane utilizing norbornane-dicarboxylic anhydride siloxane along with cyclopolydiorganosiloxane or organo terminated polydiorganosiloxane or mixtures thereof to produce norbornane anhydride substituted organosiloxane without the generation of a significant amount of cyclopolydiorganosiloxane.
The present invention is based on my discovery that 1,3-bis(norbornane dicarboxylic anhydride)tetraorganodisiloxane such as 5,5'-(1,1,3,3-tetramethyl-1,3-disiloxanediyl)-bis-norbornane-2,3-dicarboxy lic anhydride can be heated with either cyclopolydiorganosiloxane, such as octamethylcyclotetrasiloxane, or triorganosiloxy chain stopped polydiorganosiloxane, such as dimethylvinylsiloxy chain stopped polydimethylsiloxane or trimethylsiloxy chain stopped polymethylvinylsiloxysiloxane or mixtures thereof in the presence of an equilibration catalyst under neat conditions at temperatures as high as 200.degree. C. Surprisingly, no cleavage of the norbornane anhydride or organosiloxane structure results, such as silicon-carbon bonds, or anhydride bonds, while forming the norbornane anhydride substituted organosiloxane, and the formation of cyclopolydiorganosiloxane is minimized.